Scroll transducer

ABSTRACT

A free-flooding magnetostrictive scroll transducer and method of making it. The transducer construction allows free-flooding water to fill the scroll interstices, thus eliminating the need for bonding of proximate layers of magnetostrictive material with a resinous material, as considered necessary in making a conventional scroll transducer.

United States Patent [1 1 Parker 1 June 19, 1973 SCROLL TRANSDUCER [75]Inventor: David E. Parker, Pawcatuck, Conn.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

22 Filed: Jan. 6, 1972 211 Appl. No.: 215,741

[52] US. Cl. 335/215, 336/20, 336/213,

' 340/11 [51] Int. Cl. H011 21/00 [58] Field of Search 336/20, 213, 219;

' [56] kketerences Cited Y UNITE'DSTATES PATENTS 7/1949 'Smoluchowski340/11 UX 2,519,495 8/1950 Nesbitt et a1. 336/20 X 3,393,401 7/1968Meyers 340/11 3,303,449 2/1967 Stimler 336/213 Primary Examiner-Thomas JKozma Attorney-Richard S. Sciascia and Louis B. Applebaum [57] ABSTRACTA freeflooding magnetostrictive scroll transducer and method of makingit. The transducer construction allows free-flooding water to fill thescroll interstices, thus eliminating the need for bonding of proximatelayers of magnetostrictive material with a resinous material, asconsidered necessary in making a conventional scroll transducer.

5 Claims, 3 Drawing Figures PAIENIEDJIIM 9M3 SCROLL TRANSDUCER STATEMENTOF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or thereafter.

BACKGROUND OF THE INVENTION to reduce eddy currents. It was foundnecessary to use a resinous material to maintain a uniform distancebetween two adjacent layers so that the transducer will exhibit uniformcharacteristics. One such transducer is described in US. Pat. No.3,393,401 to Theodore J. Meyers. However, consolidation of themagnetostrictive material with the resinous material and curing theresinous material in theinterstices of various layers required expensivetooling. Furthermore, the vapors of the resinous materials used arehazardous to the health of fabricators.

SUMMARY OF THE INVENTION The objects and advantages of the presentinvention are accomplished by utilizing a free-flooding magnetostrictivescroll transducer wherein water is substituted for resinous materialsused for bonding proximate layers of magnetostrictive material andmaintaining a uniform spacing therebetween. The water used acts as alubricant and fills interstices between the scroll layers and alsoreduces the distance between the scroll layers. Should this waterevaporate when the transducer is in storage, the reduced sizeinterstices act as capillaries which are filled with water during ashort soaking period of the transducer. The transducer is thus operatedwith water filling the volume in between the scroll layers and thusmaking it a truly free-flooding unit.

One object of this invention is the elimination of the use of resinousmaterials (such as epoxy), materials heretofore deemed indispensable,for bonding proximate layers of a scroll type magnetostrictivetransducer and maintaining a uniform distance therebetween, thusreducing the cost of tooling.

Another object is to reduce a health hazard to fabricators byeliminating the use of a fluid resinous material which produces toxicfumes during use.

Still another object is the use of water in the interstices which,resonating with the transducer element, acts as a rigid solid duringoperation and thus improves the performance of the scroll transducers ofthis invention.

A further object is to provide structure adapted to improve thefrequency response of scroll transducers.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partlybroken away, of an electroacoustic transducer having a scroll type core,showing a preferred embodiment of the invention;

FIG. 2 is a cross section along line 2-2 of FIG. 1; and

FIG. 3 is a cross secton along line 3-3 of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT A free-flooding magnetostrictivescroll type transducer, shown in FIG. 1, is designated by numeral 10.The transducer 10 comprises a cylindrical core 12 which can be ofspherical shape. However, the sahpe of the core is not a significantpart of this invention. The core is made of a magnetostrictive material,generally a thin strip of nickel and has the same cross section all theway around. The core comprises a plurality of layers of the strip whichare designated as a group by numeral 14 in FIG. 1. A first ring 16,formed by soft welding one end 18 of the strip to the end of the firstor the innermost layer or convolution 20 of the core, defines the innerdiameter of the core. The remaining layers of the core are formed bycoiling the nickel strip around the first layer 20. These layers arespaced. The nickel strip forming the core is then placed on a heatinsulator, such as an alundum bat, and annealed at a high temperature,preferably around 800 C. This treatment gives the nickel strip desiredmagnetic properties and produces a thin coating of nickel oxide on theexposed surfaces of the strip. The nickel oxide coating is then used toelectrically insulate two adjacent layers from each other.

The inner circumference of the nickel core is then positioned andsecured on the outer diameter of a wooden mandrel (not shown in thedrawings) with each layer loosely coiled on its inner neighbor. Holdingwires are then attached to the outer tab of the nickel strip and thecore is mounted in a tightening tank (not shown in the drawings) whichis a tank having water therein to cover the loose scroll. A detergent isadded to the water in the tightening tank to act as a lubricant. Thescroll is then excited and tightened. The scroll is then removed fromthe tank, and the outer tab of the scroll is silver soldered to theproximate layer and the wooden mandrel is pulled out of the tightenedscroll. A layer 22 of epoxy impregnated fiber glass tape is thenapplied, covering the outer layer of the scroll as shown in FIG. 2.

A continuous length of a waterproof insulated conductor 24 is thentightly coiled around the magnetostrictive core, engaging the layers ofthe core 12. The two ends of the conductor are connected to signalgenerating equipment as is conventional. As shown in FIG. 3, a pluralityof interstices, such as one designated by numeral 26, are thus formedbetween two adjacent layers of the nickel strip of which the scroll ismade.

After fabrication, and prior to any acoustic evaluation, a scrolltransducer is kept submerged in water to prevent interlayer desication.However, interstitial water usually evaporates in due course of time,leaving only air between different layers. Interstitial water issupplied by immersing the transducer in water before an acousticevaluation thereof. During the course of acoustic evaluation of afree-flooding scroll transducer fabricated according to the teachings ofthis invention, it has been found that its sensitivity, transmittingfrequency response, and receiving frequency response are at least asgood as such characteristics of a conventional free-flooding scrolltransducer.

Thus a truly free-flooding transducer is described which is fabricatedby using a strip of a magnetostrictive material, such as nickel. One endof the strip is soft welded forming an inner layer and the remaininglayers are formed thereon. Before exciting and tightening the layers ofthe strip in a water tank, the strip is annealed at a high temperatureto form a coating of oxide which insulates electrically proximate layersof the strip. The tightened scroll, so formed, has interstices betweenlayers which are occupied by water instead of epoxy as in conventionaltransducers, thus making the transducer truly free-flooding. The shapeof the transducer is maintained by applying a layer of epoxy impregnatedfiber glass tape around the outermost layer of the scroll. A continuouslength of a waterproof insulated conductor is tightly coiled around thecore of the scroll and its ends are connected to a signal generatingequipment.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

I claim:

1. A free-flooding scroll type magnetostrictive transducer comprising:

a coiled core of continuous magnetostrictive strip material defining atorus, said core being of an approximately uniform cross section normalto a part of the circumference of said torus and providing a pluralityof layers having fluid filled interstices therebetween; and

a conductor toroidally coiled around said core.

2. The transducer of claim 1 wherein said conductor is waterproof andelectrically insulated.

3. The transducer of claim 2 wherein the surface'of saidmagnetostrictive material is oxidized forelectrically insulatingproximate layers of said scroll from each other.

4. The transducer of claim 2 wherein the width of said strip material issmaller than the inner diameter of said core.

5. The transducer of claim 2 wherein the magnetostrictive material isnickel.

2. The transducer of claim 1 wherein said conductor is waterproof andelectrically insulated.
 3. The transducer of claim 2 wherein the surfaceof said magnetostrictive material is oxidized for electricallyinsulating proximate layers of said scroll from each other.
 4. Thetransducer of claim 2 wherein the width of said strip material issmaller than the inner diameter of said core.
 5. The transducer of claim2 wherein the magnetostrictive material is nickel.